The present invention generally relates to wireless communications, and more particularly, to the receivers for wireless mobile terminals of wireless communication systems.
Wireless communication systems are commonly employed to provide voice and data communications to a plurality of subscribers within a prescribed geographic area For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. Recently, digital cellular radiotelephone systems such as those designated IS-54B (and its successor IS-136) in North America and GSM in Europe have been introduced and are currently being deployed. These systems, and others, are described, for example, in the book entitled Cellular Radio Systems, by Balston, et al., published by Artech House, Norwood, Mass. (1993). In addition to the above systems, an evolving system referred to as personal communication services (PCS) is being implemented. Examples of current PCS systems include those designated IS-95, PCS-1900, and PACS in North America, DCS-1800 and DECT in Europe, and PHS in Japan. These PCS systems operate around the 2 gigahertz (GHz) band of the radio spectrum, and are typically being used for voice and high bit-rate data communications.
FIG. 1 illustrates a conventional terrestrial wireless communication system 20 that may implement any one of the aforementioned wireless communications standards. The wireless system may include one or more wireless mobile terminals 22 that communicate with a plurality of cells 24 served by base stations 26 and a mobile telephone switching office (MTSO) 28. Although only three cells 24 are shown in FIG. 1, a typical cellular radiotelephone network may comprise hundreds of cells, and may include more than one MTSO 28 and may serve thousands of wireless mobile terminals 22.
The cells 24 generally serve as nodes in the communication system 20, from which links are established between wireless mobile terminals 22 and a MTSO 28, by way of the base stations 26 servicing the cells 24. Each cell 24 will have allocated to it one or more dedicated control channels and one or more traffic channels. The control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information. Through the communication system 20, a duplex radio communication link 30 may be effected between two wireless mobile terminals 22 or between a wireless mobile terminal 22 and a landline telephone user 32 via a public switched telephone network (PSTN) 34. The function of the base station 26 is commonly to handle the radio communications between the cell 24 and the wireless mobile terminal 22. In this capacity, the base station 26 functions chiefly as a relay station for data and voice signals.
FIG. 2 illustrates a conventional celestial wireless communication system 120. The celestial wireless communication system 120 may be employed to perform similar functions to those performed by the conventional terrestrial wireless communication system 20 of FIG. 1. In particular, the celestial wireless communication system 120 typically includes one or more satellites 126 that serve as relays or transponders between one or more earth stations 127 and satellite wireless mobile terminals 122. The satellite 126 communicates with the satellite wireless mobile terminals 122 and earth stations 127 via duplex communication links 130. Each earth station 127 may in turn be connected to a PSTN 132, allowing communications between the wireless mobile terminals 122, and communications between the wireless mobile terminals 122 and conventional terrestrial wireless mobile terminals 22 (FIG. 1) or landline telephones 32 (FIG. 1).
The celestial wireless communication system 120 may utilize a single antenna beam covering the entire area served by the system, or as shown in FIG. 2, the celestial wireless communication system 120 may be designed such that it produces multiple, minimally-overlapping beams 134, each serving a distinct geographical coverage area 136 within the system""s service region. A satellite 126 and coverage area 136 serve a function similar to that of a base station 26 and cell 24, respectively, of the terrestrial wireless communication system 20.
Thus, the celestial wireless communication system 120 may be employed to perform similar functions to those performed by conventional terrestrial wireless communication systems. In particular, a celestial radiotelephone communication system 120 has particular application in areas where the population is sparsely distributed over a large geographic area or where rugged topography tends to make conventional landline telephone or terrestrial wireless infrastructure technically or economically impractical.
As the wireless communication industry continues to advance, other technologies will most likely be integrated within these communication systems in order to provide value-added services. One such technology being considered is a global positioning system (GPS). Therefore, it would be desirable to have a wireless mobile terminal with a GPS receiver integrated therein.
It is therefore an object of the present invention to provide a wireless mobile terminal having a global positioning system (GPS) receiver integrated therein and which is inexpensive to manufacture and efficient in operation.
This and other objects of the present invention are provided by a wireless mobile terminal of a wireless communication system that includes a GPS receiver integrated therein for generating position data that can be transmitted by the wireless mobile terminal. It will be understood that the terms xe2x80x9cglobal positioning systemxe2x80x9d or xe2x80x9cGPSxe2x80x9d are used to identify any spaced-based system that measures positions on earth, including the GLONASS satellite navigation system in Europe. In the wireless mobile terminal, a wireless transceiver and a the GPS receiver share a frequency reference signal. There are several advantages to this configuration, including the reduction of duplicate components of the wireless transceiver and GPS receiver, lower power consumption because fewer parts are utilized, and enhanced performance of the GPS receiver because of the precision of the frequency reference signal.
In particular, according to the present invention, the wireless mobile terminal of a wireless communication system comprises a wireless transceiver and a GPS receiver, wherein the wireless transceiver and the GPS receiver share a frequency reference signal. The frequency reference signal is utilized by the wireless transceiver in signal demodulation and processing. Likewise, the frequency reference signal is utilized by the GPS receiver in signal demodulation and processing.
In accordance with an aspect of the present invention, the frequency reference signal shared by the wireless transceiver and the GPS receiver is a reference oscillator signal generated, for instance, by a temperature compensated reference crystal oscillator. The reference oscillator signal may be multiplied or divided by a first integer to produce a first GPS local oscillator used in signal conversion to a first intermediate frequency in the GPS receiver. Further, a second conversion stage can be incorporated in the GPS receiver by multiplying or dividing the reference oscillator signal by a second integer (which can include 1) to produce a second GPS local oscillator used in signal conversion to a second intermediate frequency in the GPS receiver. The reference oscillator signal can be further utilized at the GPS receiver by dividing or multiplying the reference oscillator signal by a third integer (which can include 1) to produce a frequency used in signal processing, for instance, as an analog-to-digital sampling signal. The wireless transceiver, on the other hand, may include a frequency synthesizer that utilizes the reference oscillator signal as a frequency reference signal. It is noted that the accuracy of the reference oscillator signal can be increased by synchronizing the reference oscillator signal with a signal from a base station of the wireless communication system, thus reducing the signal processing required for the GPS receiver.
In another aspect of the present invention, the frequency reference signal shared by the wireless transceiver and the GPS receiver is a radio frequency signal generated, for instance, by a local oscillator of the wireless transceiver. The radio frequency signal can be multiplied or divided by a first integer to produce a first GPS local oscillator used in signal conversion to a first intermediate frequency in the GPS receiver. Further, the radio frequency signal may be multiplied or divided by a second integer to produce a second GPS local oscillator used in signal conversion to a second intermediate frequency in the GPS receiver. The GPS receiver may further utilize the radio frequency signal by dividing or multiplying the radio frequency signal by a third integer to produce a frequency used in signal processing, such as an analog-to-digital sampling signal. The wireless transceiver, on the other hand, may utilize the radio frequency signal for another signal processing function within the wireless transceiver, such as but not limited to a transmit carrier signal. The radio frequency signal may be taken from the output of a frequency synthesizer of the wireless transceiver. Thus, the frequency synthesizer of the wireless transceiver may operate alternately in a wireless mode and a GPS mode.
In yet another aspect of the present invention, the frequency reference signal is a radio frequency control signal generated, for instance, by a phase locked loop circuit of the wireless transceiver. The radio frequency control signal is utilized by the GPS receiver to control the operation of a GPS local oscillator, and is used by the wireless transceiver to control the operation of a wireless transceiver local oscillator. At the GPS receiver, the GPS local oscillator outputs a GPS frequency signal that is multiplied or divided by a first integer and used in signal conversion to an intermediate frequency. Further, the GPS frequency signal may be multiplied or divided by a second integer used in signal conversion to a second intermediate frequency. The GPS frequency may also be divided or multiplied by a third integer to produce a frequency used in signal processing, for instance, as an analog-to-digital sampling signal. The cellular local oscillator, on the other hand, outputs a wireless frequency signal that is used by the wireless transceiver for another signal processing function within the wireless transceiver, such as but not limited to a transmit carrier signal. The phase locked loop circuit of the wireless transceiver may include a frequency synthesizer that operates alternately in a cellular mode and a GPS mode.
In yet another aspect of the present invention, a method for sharing a frequency reference signal between a wireless transceiver and a GPS receiver in a wireless mobile terminal comprises the steps of generating a frequency reference signal by said wireless transceiver, and providing the frequency reference signal to said GPS receiver.
In addition, the above method can include the step of multiplying the frequency reference signal by an integer value for use in signal processing at the second subsystem. Similarly, the above method can include the step of dividing the frequency reference signal by an integer value for use in signal processing at the second subsystem. Further, the above method can include the step of alternating the operation of the frequency synthesis mechanism between a wireless transceiver mode and a GPS mode.
Accordingly, it can be readily appreciated that a wireless mobile terminal of the present invention will have numerous advantages, a few of which are delineated below.
First, a wireless mobile terminal in accordance with the present invention would be particularly advantageous in tracking articles using wireless communication systems which are fairly ubiquitous. Examples of articles that can be tracked in such a manner include railroad boxcars, barges, or trucks used in transporting goods, stolen automobiles, and persons. By placing a call to the wireless mobile terminal with a request for position data set forth in a predefined format, the wireless mobile terminal can gather such information from the associated GPS receiver and transmit the position data back to the requesting entity. This feature may be particularly desirable in combination with a telemetry system, as will be appreciated by those knowledgeable in the many applications of telemetry.
Second, the wireless mobile terminal would be particularly advantageous in the provision of enhanced 911 (E911) services. An E911 system that includes a GPS receiver would be advantageous in many situations, such as in an automobile accident wherein a 911 call is automatically initiated so that the occupants of the automobile can communicate their condition and request appropriate assistance. In such a circumstance, the location of the automobile may also be sent automatically to the 911 operator in order to minimize the response time and to locate the accident scene if the occupants are unconscious or unable to effectively communicate their location to the 911 operator.
Third, a wireless mobile terminal in accordance with the present invention would be particularly advantageous in allocating resources of a wireless communication network since the location of the user is known. For example, in a celestial wireless communication system, a satellite could use pencil beams for transmitting signals to a wireless mobile terminal rather than transmitting to a relatively large area. This would result in reduced energy consumption by a satellite and greater spectral re-use of the available frequency band. The same results of reduced energy consumption and greater spectral re-use can also be realized in a terrestrial wireless communication system wherein the location of a user within a cell is known.
Fourth, a wireless mobile terminal in accordance with the present invention would be particularly advantageous in that it has a reduced number of duplicate components, and thereby, has a lower cost, consumes less power, and is smaller.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein in the scope of the present invention, as defined by the appended claims.